I cannot use PSE8's distortion/vignetting filter on grayscale TIFF images created by an Epson 3200 scanner from a 4x5 B&W negative. Anyone know what I should do? It worked yesterday but now it doesn't work.

Software's Epson Scan downloaded from Epson's support site. I set up the scanner for B&W negative, 3200 lpi scan resolution, 16 bit grayscale.